Bottom Line:
A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation.The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs.The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis.

ABSTRACTLung radiotherapy is greatly benefitted when the tumor motion caused by breathing can be modeled. The aim of this paper is to present the importance of using anisotropic and subject-specific tissue elasticity for simulating the airflow inside the lungs. A computational-fluid-dynamics (CFD) based approach is presented to simulate airflow inside a subject-specific deformable lung for modeling lung tumor motion and the motion of the surrounding tissues during radiotherapy. A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation. The lung is modeled as a poroelastic medium with subject-specific anisotropic poroelastic properties on a geometry, which was reconstructed from four-dimensional computed tomography (4DCT) scan datasets of humans with lung cancer. The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs. The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis.

Mentions:
Phasic pressure with a period of 4 s is imposed at the inlet to the lobe as illustrated in Figure 5. The amplitude of the pressure waveform was prescribed based on spirometry studies acquired from M.D. Anderson Cancer Center, Orlando. The property data (beside the YM) were assumed from those established in previous studies. The Poisson ratio v in the poroelastic governing equation was assumed to be 0.4, which falls within the range (0.25–0.47) suggested in previous studies [22, 23]. The density of lung was assumed to be 700 kg/m3 [21]. Preliminary studies indicated that the deformation is little affected by the permeability k over the range (0.01–0.1) as expected. The anisotropic YM adopted from a previous study based on optical flow registration patient data ranged from 10 Pa to 500 Pa. The high YM values correspond to either the tumor location where the structure is rigid or the main trachea wall where the tissue is thick and rigid. The average YM for the whole lung is 178 Pa. This average value is used for the reference cases utilizing linear elastic property. Figure 6 shows representative color-coded YM distribution on a 2D slice of lobe obtained from optical flow registration and used for the anisotropic elasticity calculations in this paper [13].

Mentions:
Phasic pressure with a period of 4 s is imposed at the inlet to the lobe as illustrated in Figure 5. The amplitude of the pressure waveform was prescribed based on spirometry studies acquired from M.D. Anderson Cancer Center, Orlando. The property data (beside the YM) were assumed from those established in previous studies. The Poisson ratio v in the poroelastic governing equation was assumed to be 0.4, which falls within the range (0.25–0.47) suggested in previous studies [22, 23]. The density of lung was assumed to be 700 kg/m3 [21]. Preliminary studies indicated that the deformation is little affected by the permeability k over the range (0.01–0.1) as expected. The anisotropic YM adopted from a previous study based on optical flow registration patient data ranged from 10 Pa to 500 Pa. The high YM values correspond to either the tumor location where the structure is rigid or the main trachea wall where the tissue is thick and rigid. The average YM for the whole lung is 178 Pa. This average value is used for the reference cases utilizing linear elastic property. Figure 6 shows representative color-coded YM distribution on a 2D slice of lobe obtained from optical flow registration and used for the anisotropic elasticity calculations in this paper [13].

Bottom Line:
A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation.The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs.The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis.

ABSTRACTLung radiotherapy is greatly benefitted when the tumor motion caused by breathing can be modeled. The aim of this paper is to present the importance of using anisotropic and subject-specific tissue elasticity for simulating the airflow inside the lungs. A computational-fluid-dynamics (CFD) based approach is presented to simulate airflow inside a subject-specific deformable lung for modeling lung tumor motion and the motion of the surrounding tissues during radiotherapy. A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation. The lung is modeled as a poroelastic medium with subject-specific anisotropic poroelastic properties on a geometry, which was reconstructed from four-dimensional computed tomography (4DCT) scan datasets of humans with lung cancer. The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs. The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis.